ISO 6437:1984

Overview

ISO 6437:1984 specifies a titrimetric method for the determination of the total chromium content in copper‑chromium alloys listed in International Standards. The procedure is applicable to products containing 0.10–2.00 % (m/m) chromium. The standard describes principle, reagents, apparatus, stepwise procedure, result expression and reporting requirements. A laboratory safety note stresses normal precautions for the use of perchloric acid.

Key topics and technical requirements

• Analytical principle: Dissolve a test portion, oxidize chromium with perchloric acid in the presence of orthophosphoric acid (to prevent chromium loss), oxidize any residual Cr(III) with potassium permanganate, reduce chromium(VI) with iron(II) (iron ammonium sulfate), and determine the equivalence point by volumetric (indicator) or potentiometric titration.
• Applicable range: Chromium content from 0.10 to 2.0 % (m/m).
• Reagents (selected): hydrochloric, nitric, hydrofluoric, perchloric and orthophosphoric acids; potassium permanganate; potassium dichromate standard (for standardization); diphenylamine indicator; iron ammonium sulfate titrant.
• Apparatus: routine laboratory glassware (600 ml tall beakers), titration setup and optional potentiometric electrodes for endpoint detection.
• Standardization & controls: daily standardization of the iron ammonium sulfate solution is required. A check test using a certified standard material or synthetic sample of known chromium content is prescribed to validate the method.
• Result calculation: chromium percentage is calculated from the volume of titrant used, the titre of the iron solution (expressed as mg Cr per ml) and the mass of the test portion, as specified in the standard.
• Reporting: sample identification, method reference, numerical results and expression, any atypical observations, and any operations not covered in the standard must be included in the test report.

Applications and users

• Quality control and acceptance testing of copper-chromium alloys in manufacturing and procurement.
• Metallurgical and analytical chemistry laboratories performing elemental analysis of copper alloys.
• Suppliers, inspection bodies and conformity assessment labs verifying compliance with alloy specifications in international and national standards.
• R&D teams assessing alloy composition during alloy development or failure analysis.

Related standards

• ISO/TC 26 (Copper and copper alloys) publications and International Standards that list specific copper-chromium alloys and sampling methods may be used alongside ISO 6437 for complete material verification.

Keywords: ISO 6437, copper alloys, chromium determination, titrimetric method, potentiometric titration, perchloric acid, potassium permanganate, iron ammonium sulfate, metal quality control, analytical chemistry.